Another thing that is not in most references as to this disease, even when I talked to the vets is that you can move the birds from the contaminated clean disinfected flight and STILL lose all the birds. What I learned after the fact that if I had also washed and disinfected all of the birds feet that I moved to the supposedly disinfected flights, I could have stop the progression of infection. How 1 bird contaminates another if they are in a flight is by their feet as they perch on the food/water bowls or perches. The next bird that perches in the same area gets contaminated. I also learned that it is NOT air-bourne. Birds can be housed up to 2 feet away from a contaminated flight or cage and not be affected.
As to cockatiels the only ones I found that were resistant were lutino, fallow, and splits to either of these mutations. Both mutations were developed in FL, thus I suspect that may be the reason why.